Anisotropic rotational reorientation of perdeuterated 2,2,6,6-tetramethyl-4-piperidone N-oxide in jojoba oil: An ESR line shape study

A detailed ESR line shape study of perdeuterated 2,2,6,6-tetramethyl-4-piperidone N-oxide (PD-Tempone) in jojoba oil has been performed on desktop computer utilizing on-screen simulation. A detailed description of the procedure is presented. The uniqueness of such computer fitting is demonstrated. An analysis employing anisotropic rotational diffusion at the fast motional narrowing region (τ_R ≤ 10^-11 s) suggests that PD-Tempone exhibits asymmetric rotational diffusion with N = 3.3 at an axis z′ = Y in the plane of the molecule and perpendicular to the N-O bond direction. The anisotropic interaction parameter κ has been determined to be 0.018. The ε parameter for correction to the nonsecular Debye spectral densities is found to correlate with the ansiotropic interaction parameter κ. Larger ε value seems to correlate with smaller κ value. Both observations are interpreted as small solute experiencing steric hindrance in large solvent molecules which results in preferential orientation. The precision of the parameters N and ε and the uniqueness of the simulation are discussed.